The Dark Side of the Moon

Beacon Station Nine was the last lighthouse between Earth and the outer colonies, and it was held together, as far as Captain Amara Obi could tell, by duct tape, prayer and the stubbornness of six people who had nowhere else to go.

Its light was not a light at all, not in the old sense. It was a pulse of navigation data, sent out every eleven seconds in every direction, so that the long-haul freighters crossing the black between Mars and Ceres would know where they were and where the rocks were not.

If the beacon went dark, ships would drift. If ships drifted, people would die. It was, Amara often reminded her crew, the only job in the solar system simpler to explain than to do.

On the morning of the seventy-third day of their rotation, the beacon skipped a pulse.

It was only one. Eleven seconds, then twenty-two, then eleven again, as regular as a heartbeat. But in the control ring the six keepers looked up from their breakfasts and their screens and their sleep, all at once, like birds hearing a hawk.

“Diagnostics are clean,” said Obi’s engineer, Petrov, after a long minute. “Nothing wrong with the transmitter.”

“Then why did it skip?”

Petrov pulled up the log. His face, lit blue by the screen, went very still. “It didn’t,” he said. “Something else sent a pulse at the same moment. On our frequency. From the other side of the Moon.”